A common site of orthopedic trauma in humans occurs in the hands, due in part to the natural reflex to put one's hands out during a fall to absorb the impact of the fall. Of the bones in the hand, the scaphoid is commonly fractured during these traumatic events due to its location within the hand. To repair scaphoid fractures, compression screws can be utilized to compress and hold the bone fragments together while the body's natural healing process fuses the fragments back together.
One particular type of compression screw that is commonly used to hold scaphoid bone fragments together is a headless compression screw. As opposed to traditional compression screws, the headless compression screws forego the head portion of the screw, which is typically formed at one end of the screw and compresses on the cortical shell of the scaphoid to compress the fragments together. By using headless compression screws rather than traditional compression screws, the entirety of the compression screw can rest inside the cancellous bone of the scaphoid as the bone heals.
Since the entire compression screw rests within the scaphoid when using a headless compression screw, the length of the headless compression screw is of utmost importance to the success of the repair procedure. If the screw is too long, a portion of the screw will rest outside of the cancellous bone and may stick out past the outer surface of the scaphoid, which can cause damage to surrounding soft tissues. If the screw is too short, the screw will not achieve sufficient purchase within the cancellous bone to hold the bone fragments together, which can allow for the bone fragments to separate from each other and render the screw useless. To overcome this problem, various methods and devices have been utilized to attempt to allow a user to select the proper headless compression screw length.
One such method involves placing a Kirschner wire (k-wire) within the scaphoid across the scaphoid's length and sliding a depth gage over the k-wire until the tip of the depth gage touches the outer surface of the bone. The depth gage therefore measures the entire length that the k-wire has penetrated into the scaphoid, with a predetermined value being subtracted from the measurement to come up with the screw length that should be used. A second method to determine the length of the compression screw involves placing a k-wire within the scaphoid, similar to the first method, and then pressing a second k-wire of equal length against the outer surface of the scaphoid adjacent to the entry hole of the first k-wire. The k-wires are then aligned so that a measurement can be taken to determine the length difference between the k-wires, which should approximate the length of the first k-wire that is in the scaphoid.
The current practice is to select a screw for implantation that is 2 to 4 millimeters shorter than the measured distance, to account for various difficulties associated with measurement of the scaphoid such as the asymmetrical nature of the scaphoid, difficulty visualizing the screw's eventual placement within the scaphoid, and the fragments typically being separated when the measurement is taken. This practice of “selecting short” can lead to a compression screw being selected that is too short and many users complain that the current practice makes it difficult to precisely select the proper headless compression screw length.
What is needed in the art is a device and method for selecting the appropriate length of a headless compression screw to hold scaphoid bone fragments together that gives more consistent and accurate measurements than known devices and methods.